Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
There is considerable interest in making complex holey structures that can subsequently be drawn into a microstructured fibre. This is currently done by stacking and fusing capillaries or canes.
Photonic crystal fibres are commonly made in glass. The fabrication technique used is capillary stacking with thermal fusing. The general technique used has been to use glass canes or capillaries having a single central hole. Canes are solid rods, without any internal holes, whilst capillaries are elongated structures that have one or more holes running through them. The capillaries used to date have usually been of circular cross-section, and had a single central hole. There have been a number of examples in which holes of different sizes were combined in one structure, but this has generally proved difficult because the self-packing properties of same-sized rods and canes breaks down when different diameters are used. In this case there is a need to “pack” the structure to support it, and prevent it collapsing. Maintaining the hole structure in glass holey fibres is very difficult, and requires a high degree of control over both the preform fabrication and drawing processes. It is likely that for this reason very few structures that deviate from the same-sized canes or single holed capillary stack have been reported. In addition, any deviation from the single central holed capillary requires control of the rotational orientation of the capillary.
Whilst attempts have been made to use glass canes and capillaries of hexagonal cross-section with multiple holes, difficulties with fusing and distortion have been encountered resulting in poor quality fibre.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.